Method and apparatus for separating waste particles from media used in sandblasting



Dec. 14, 1954 METHOD Filed June 7, 1949 E. R. LJUNGDELL. ET AL ANDAPPARATUS FOR SEPARATING WASTE PARTICLES FROM MEDIA USED IN SANDBLASTING 2 Sheets-Sheet 1 lNVENTORS ERIK RAGNAB LJUNGDELL KARL GUSTAVEVERT KRANTZ ATTYS.

D 1954 E. R. LJUNGDELL ET AL 2,696,910

METHOD AND APPARATUS FOR SEPARATING WASTE PARTICLES FROM MEDIA USED INSAND BLASTING Filed June 7, 1949 2 Sheets-Sheet 2 FIG. 2

INVENTORS 5am RAGNAR LJUNGDELL KARL GUSTAV EVERT KRAN'TZ ATTYS.

United States Patent METHOD AND APPARATUS FOR SEPARATING WASTE PARTICLESFROM MEDIA USED IN SANDBLASTING Erik Ragnar Ljungdell, Bofors,Karlskoga, and Karl Gustav Evert Krantz, Stockholm, Sweden, assignors toAB Svenska Flaktfabriken, Stockholm, Sweden, and AB Bofors, Bofors,Karlskoga, Sweden Application June 7, 1949, Serial No. 97,622

Claims priority, application Sweden June 9, 1948 Claims. '(Cl. 209-139)The reason for blasting a surface, however, is not always for cleansingpurposes, but blasting is also used to improve the surface qualities bybombarding the surface by for instance shots or other media.

In the following the word sand is used to indicate the blasting media,it being understood that the term is intended to include all kinds ofblast media used. Compressed air is the usual driving force for the sandbut this force can be replaced by mechanical or other means which throwthe sand against the object to be treated, itbeing pointed out that theuse of the term blast media is not limited to compressed air, but canalso comprise media other than compressed air.

In the cases described above the sand is discharged by means ofcompressed air or centrifugal forces with great speed from a deviceagainst the objects which are to be cleansed or treated in any otherway. Then, in both cases, the sand will be mixed with particles removedfrom the objects or from the sand itself. For economical reasons thesand has to be collected and used once more, when the deteriorationshave been removed to the greatest possible extent.

With cleansing sand, which has been used for blasting of cast steel, ithas proved impossible to separate the main part of the fine dust fromthe blast media by the methods available. Consequently, the quantity offine dust usually increases in proportion to the time during which thesand has been used. This has made it necessary to take away thecirculating sand now and then from the circulating system of thecleansing apparatus, in order to let it pass a separate treatment, inorder to remove the dust, when the proportion of same is too high. Thisinvolves expenses and loss of time in the production. In this case thedust consists of fine particles of burnt molding sand and scales andfragments of worn-out grains of sand. Among other things the dust causesdecreasing efficiency of the blast and, further, the dust is unhealthyand complicates the blasting as it makes it difiicult to observe thepiece worked on and to judge the result of the blasting during the work.

The present invention provides a new possibility of cleansing the sandfrom dust, which in practice makes the blasting operation more efiicientand healthy and also makes the use of the sand more economical, as thecleansing of the sand, for instance, can be carried out continuously.The method is based on mixing an air current with a current of thecleansing medium, so that the air current meets the current of the sandand changes the direction of those particles, which are to be separated.The speed and direction of the air current is then adjusted so'that thedifference in the moving energy between the particles-0f different sizeand weight is made use of when changing the direction of movement of theparticles to be separated, whilst the necessary particles above acertaln size are not affected. The separation .a hole 34 therein.

2,696,910 Patented Dec. 14, 1954- ICC might then be made in a section ofthe conveying system of the cleansing apparatus for the cleansingmedium, so that the cleansing apparatus can work continuously with acirculating cleansing medium.

From experiments on technical scale on operating conditions with a sandblast apparatus, which worked with a quantity of steel sand of kg. perminute, it has been found that all dust particles with a particle sizesmaller than 640a (0.64 mm.) could be separated from the steel sand bythe use of the new cleansing method. The quantity of collected dust wasabout 9% of the weight of the steel sand.

The method of cleansing the sand will now be described with reference tothe drawings attached hereto, showing an embodiment of an arrangementaccording to the invention.

Fig. 1 shows schematically a blast arrangement with the cleansingarrangements for the sand and the air; and Fig. 2 shows a horizontalview of the blast cabinet in greater scale.

Referring to the drawings, 1 is the sand blast cabinet and 2 indicatesthe blast worker, 3 is a blast pipe and 4 represents castings to beblasted, placed on a car 5. The car is resting on a rotatable disc 6,which is driven by an electrical motor 8 by means of a change speed gear7. While the disc 6 is slowly rotated, the jet with the blast medium isdirected at the objects 4 cleansing the objects. Reference numeral 9indicates an exhausting opening for the air mixed with dust, which isproduced in the blast cabinet 1 and 10 indicates a suction duct to thedust separator 11, which is of so called tube-filter type. 12 is a dustcontainer for gathering the dust separated from the dust separator 11and 13 is an outlet for the separated dust from container 12. 14 is asuction fan or any other suction-apparatus for withdrawing cleansed airfrom the dust separator 11. 15 indicates an electrical motor for drivingthe fan 14 and 16 indicates an exhaust nozzle for the cleansed air.

The revolving disc 6 is provided with apertures 17, through which theblast medium together with the impurities in the form of slag, scales,burned sand and the like descends to a chamber 18, in which ascrewconveyor 20, driven by the motor 19, convey the contaminated mediumto the pocket 21. In this pocket 21 the medium is seized and is liftedby an endless bandconveyor 23 provided with scoops 22. This conveyor isof known type and brings the material to the tipping chute 24, fromwhich the material falls down into a rotating sifting drum 25, driven byan electrical motor 26. The sifter 25 is so arranged that the sand andsmaller particles can pass the holes or meshes of the sifter and falldown in the shoot 27, while larger particles as spikes etc. pass in theaxial direction through the shifting drum 25 and are tipped through theoutlet opening 28'.

The real purifying arrangement according to the invention consists, inaddition to the tube or plunge tube 27, of a vertical pipe or tube 29.The tube 29 has a lower open end 30 and likewise an open upper end '31between which the pipe 27 connects. The lower part of the end 30 isenclosed by and opens into a low pressure chamber 32 provided withaconical bottom 33 having The hole 34 co-operates with a lock valve 35which conveniently is springloaded. To the low pressure chamber 32 isconnected a pressure fan 36, which introduces fresh air in the chamber32. The fan 36 is driven by an electrical motor not shown. The tube end30 has a side wall 37, which is adjustable so that the free flowing areaof the tube end may be increased or decreased. For this purpose the sideWall 37 is provided with an outer flange 38 having slots 39 for bolts(not shown) arranged in the wall 40 constituting a fixed part of thechamber 32. The side wall 37 is thus displaceable along the slots and isfastened in different positions by means of bolts and nuts.

When the fan 36 is in operation the contaminated sand falling downthrough the plunge tube 27 meets a stream of air from the fan 36 in thetube end 30, the force and velocity of the air being adjusted to carryaway the impurities in the sand but not the sand itself (the cleansingmedium) and conveys these impurities out 3 through the upper pipe end 31to a dust separator 41. The cleansing medium or the sand on the otherhand falls down into the chamber 32 and is collected there in asubstantially clean condition.

The dust separator 41 consists of a hose filter the lower chamber 42 ofwhich receives the separated deteriorations, falling down from saidchamber into transportable dust containers 43. The purified air passingthrough the filter hoses 44 is exhausted by suction by means of afan 45,driven by an electrical motor 46, and continues through a pipe 47. Inthe pipe 47 a valve 48 is arranged, regulated by a motor 49 for apressure regulator 50 for regulatingv the velocity of air. The pressureregulator 50 is used for regulating the air velocity in the tube end 30.It is important that the fan always exhausts more air than isforced inby the The difference in air volume is taken in through the opening 28and the pipe 27. The regulator 50 opens and shuts the valve 48- independence on the choking of the hose filters 44 in such a way that thevalve 43 is opened more by increased choking of the filter 44 and ispowerfully throttled by newly cleaned filters 44. j The purified air inthe tube 47 is led to the blasting chamber 1 and is distributed by atube 51 to special nozzles 52, which constitute an air curtain of blownair in the blast chamber as a protection for the blast operator 2against the whirling dust and sand in the chamber 1. A throttle 53 inthe tube 47 regulates the quantity of air to the tube 51. The surplus ofair is led into a shunt 54, which is connected to the tube 10. As air isexhausted from the chamber 1 through the tube 10, it is necessary toprevent the evacuation of the chamber 1. The chamber is thereforeprovided with openings 551, which admit air from out side the chamberinto the chamber 1.

Under the chamber 32 there is a high pressure chamber 55, in whichv thecleansed steel sand or the cleansing medium 56 is collected in order tobe conveyed from there by means of compressed air to the blast jet 3. Ifthe valve is spring-loaded it keeps the opening 34 closed until theweight of the steel sand conteracts the spring and opens the valve 35,when the sand falls down into the chamber 55. Alternatively the valve 35can be air pressure loaded. In the latter case a compressed air duct 57is drawn over a valve 58 and a duct 59 into the chamber 55. Then the airpressure in the chamber must be higher than in the chamber 32. The valve58 is controlled by a bar 60 for the passing on the air partly to theduct 59 and partly to a shunt 61 from same, leading to the blast jet 3.The shunt or duct 61 goes through a high pressure ejector 62, connectedto the bottom of the chamber 55, through which the air current in duct61 transports the steel sand or other purified cleansing medium from thechamber 55 and ejects this through the blast jet 3. The blaster 2 isplaced in a separate part of the blast chamber 1, to which there is adirect door 63, whilst the truck 5 is led into the blast chamber boxthrough an opening, which is shut by the doors 64 and 65.

While in the foregoing a preferred embodiment of the invention has beendescribed and shown it is to be understood that the method and.arrangement is susceptible of any alterations and modifications whichfall within the scope of the appended claims. The current of air, which,

is directed against the cleansing medium to be purified,

thus ought not to be directed exactly against the movement direction ofthe cleansing medium. It is important that each current has a directiondeviating from that of the other one, so that when the currents meet,the air current can pass through the current of the cleansing A mediumand from this can blow away through a convenient outlet such impurities,which as regards its mass are of such a light character that thesedeteriorations, but not the cleaning medium, are separated from thecurrent Having now described our invention, what we claim as new, anddesire to secure by United States Letters Patent, is:

1. In the method of separating dust and other waste particles from sandand like media used in sand blasting,

the steps which comprise introducing a stream of waste sand blastingmedium into a chamber located between a lower zone maintained at apredetermined pressure above atmospheric and an upper zone maintained atsuction pressure, causing a current of air under predetermined positivepressure to pass through said chamber from said lower zone to said upperzone at a predetermined veloc- 35 ity in a direction to engage and passthrough said stream of waste blast medium to entrain and carry off tothe upper zone the waste particles in the medium having a size andweight less than the sand particles of the medium which are caused topass into the lower zone, filtering from the current of air in thesuction zone the entrained waste particles, and regulating the suctionpressure at the downstream side of the filter in correspondence to thedegree of blockage of the filter to maintain substantially constant thevelocity of the current of air passing through said chamber.

2. in apparatus for separating waste particles from sand and like mediaused in sand blasting, a generally upstanding tube having intermediateits ends an inlet for a stream of waste sand blast medium, meansincluding an exhaust fan to create a suction pressure zone at the end ofthe tube above said inlet, blower means to maintain air under positivepressure at the lower end of the tube to cause a stream of air to passcontinuously upward through said tube at a predetermined velocity andthrough the stream of waste sand medium to entrain and carry offtherewith to the suction zone the waste particles in the medium having asize and weight less than the sand particles of the medium which passdownwardly in the tube, filter means in the path of travel of the airstream through said suction zone operable to remove from the air streamthe entrained waste particles, and means to control said exhaust fan andthereby regulate the suction pressure at the downstream side of saidfilter in correspondence to the degree of blockage thereof to maintainsubstantially constant the velocity of the stream of air passing throughsaid tube.

3. Apparatus as claimed in claim 2 wherein a section of the wall of thetube portion below the waste stream inlet is mounted for slidingadjustment in a direction normal to the tube axis to vary the free flowarea through said portion.

4. in apparatus for separating waste particles from sand and like mediaused in sand blasting, means defining an operating station having anopening of substantial size confronting the zone in which work is sandblasted, a generally upstanding tube adjacent said sand blast work zoneand having intermediate its ends an inlet for a stream of waste sandblast medium, means including an exhaust fan to create a suctionpressure zone at the end of the tube above said inlet, blower means tomaintain air under positive pressure at the lower end of the tube tocause a stream of air to pass continuously upward through said tube at apredetermined velocity and through the stream of waste sand medium toentrain and carry off therewith to the suction zone the waste particlesin the medium having a size and weight less than the sand particles ofthe medium which pass downwardly in the tube, filter means in the pathof travel of the air stream through said suction zone operable to removefrom the air stream the entrained waste particles, means to control saidexhaust fan and thereby regulate the suction pressure at the downstreamside of said filter in correspondence to the degree of blockage thereofto maintain substantially constant the velocity of the stream of airpassing through said tube, and means to discharge the filtered air underpositive pressure as a protective curtain in the opening of saidoperating station.

5. In sandblast apparatus, a separating chamber comprising a tubularmember having an upper portion defining a suction zone and a lowerportion defining a positive pressure zone, means to create a suctionpressure in the upper portion of the tubular member, means to maintain apositive pressure in the lower portion of said tubular member and causea stream of air to pass continuously upward through said tube at apredetermined velocity, inlet means for a stream of waste sandblastmedium opening angularly downward into said tubular member intermediatesaid upper and lower portions thereof and having a rounded wall surfaceconnecting the adjacent portions of the inlet and the upper portion ofthe tubular member, said inlet introducing the waste medium counter tothe flow of said air stream to cause the latter to entrain and carry toand through the suction zone of the tubular member the waste particlesin said medium of less than a predetermined size and weight, means toreclaim the waste sandblast medium from the sandblast apparatus anddeliver same to said inlet means, means mounting a section of the wallof the lower portion of the tubular member below the waste medium inletfor movement radially of the tube to thereby selectively adjust the freeflow area of the lower portion of the tubular member, means including afilter for recirculating the separated medium from the suction zone ofthe tubular member to the sandblast apparatus, and means to regulate thesuction pressure in the upper portion of the tubular member incorrespondence to the degree of blockage of the filter to maintainsubstantially constant the velocity of the air stream passing throughsaid tubular member.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 312,333 Crow Feb. 17, 1885 513,123 Marmon Jan. 23, 1894519,958 Huefiner et a1. May 15,1894

Number Number Name Date Zoller May 29, 1906 Gray June 23, 1908 DavisApr. 23, 1918 Plaisted July 9, 1918 Stebbins Jan. 6, 1925 Stebbins Apr.12, 1927 Stebbins Apr. 17, 1928 Hull Apr. 23, 1929 McLean Apr. 19, 1932'Piek Nov. 1, 1932 Lechthaler et a1. June 10, 1947 La Pointe Aug. 31,1948 FOREIGN PATENTS Country Date Germany July 4, 1911 Germany July 4,1935

